Progress of automated control requires higher safety and reliability of electronic control devices. In the event of an abnormality, immediate detection of the abnormality is required to stop operation in order to secure safety of electronic control devices.
In addition, it is required not only to reliably stop operation in the event of failure for safety, but also to continue the operation after safety is secured. For example, since an electric power steering system has been used in a large-size vehicle with larger weight as improved in performance, stopping its operation in the event of failure causes large steering force to be manually generated. Thus, the operation needs to be continued even in the event of failure after safety is secured.
As a technique for continuing operation of an electric power steering system even in the event of failure, for example, PTL 1 (JP 2012-161154 A) discloses a technique for allowing a motor to include a pair of coils so that the pair of coils is driven by a pair of inverters. PTL 1 also discloses a technique for reducing ripple current by applying an offset to a duty cycle of PWM modulation of the pair of inverters, as well as for reducing imbalance of heat loss by changing the offset depending on a steering state.